This invention relates to an enclosed electrical contact assembly and particularly to a contact assembly adapted for operation in environments including airborne particles.
U.S. Pat. No. 4,927,988 was issued May 22, 1990 to the present inventor and discloses a centrifugal switch assembly for controlling of electric motors in which the contact assembly is enclosed to prevent adverse affects from airborne contaminants including chemical substances, foreign particles and the like. As more fully disclosed in such patent as well as the prior art cited during the prosecution thereof, various systems have been provided for enclosing of the contact gap between contacts in various switch units. In particular, a flexible boot unit is often connected to the respective mounting elements for the contacts to shield the enclosed gap between the contacts and the contact surfaces from environmentally airborne foreign substances.
As most fully disclosed in the '988 patent, the opposed contacts include a first contact mounted essentially as a fixed contact and the opposing contact mounted on leaf spring support for movement into and from engagement with the fixed contact. A centrifugal actuator is selectively coupled to the movable contact leaf spring support for opening and closing of the contacts and, in particular, to provide a forced closing and a snap action release as a result of the mounting of the movable contact. The enclosure included a convoluted boot member having a first tubular portion secured to the movable contact by an interference fit and a second tubular mount portion encircling the fixed contact and spaced therefrom, with a pressurized engagement between the tubular portion and the fixed support structure. Thus, the mounting and actuation of the movable member maintained firm interengagement of the second tubular portion with the fixed support structure.
The inventor's laboratory testing has found a significant improvement in performance and expected life with the subject switch design compared to the prior art switch enclosures. The improvements focused on eliminating the entry of foreign debris into the protective enclosure either during the assembly process or during the application of the product. The improvements included: an improved seal of the boot structure to the contacts, a structure which allows release of internal pneumatic conditions resulting from the more effective seal of the enclosure about the contacts, and improved assembly and storage procedures to maintain clean components.
The prior art as cited in the Nolte patent discloses other systems wherein an enclosure is otherwise formed with various interconnections between the enclosure and the opposing contacts. For example, Seagraves U.S. Pat. No. 3,015,011 discloses a boot structure with offset tubular portions, one of which telescopes over one contact and is secured thereto by an interference fit, with the opposite enclosure end projecting into a separate cup-shaped member overlying the opposite contact. A similar total enclosure is shown in U.S. Pat. No. 4,922,066 which issued May 1, 1990. Other dust proof switches are shown in the other references cited in the several patents discussed.
The prior art is not considered to disclose either the problems found by Applicant or a structure which will eliminate such problems.